An agitator mill of this type is known from U.S. Pat. No. 3,780,957, wherein the separating device consists of one or more so-called screen cartridges, i.e. screens with a circular cylindrical cross-section, which protrude into the grinding chamber. From U.S. Pat. No. 4,739,936 it has become known to provide these screen cartridges with a relatively flat cross-section, i.e. with an approximately elliptical cross-section or with a cross-section with walls which are parallel to each other. The basic shape of the screens is as usual cylindrical, but is not anymore circular cylindrical.
From DE 35 21 668 A an agitator mill is known, the agitator shaft of which having at its free end a hollow space, into which a separating device in the shape of a cylindrical screen protrudes. In this separating device a mixing body is arranged, which can be cooled.
From DE 22 34 076 C3 an agitator mill is known, the separating device of which is disposed at the agitator shaft itself and rotates with the latter. Within this separating device, which separates the grinding bodies, at least one scraper is provided, in order to prevent clogging of the separating device during the treatment of thixotrope fluids.
All the above-described separating devices have in common that the passage openings for the grinding stock must be very small, as the separating devices should retain the auxiliary grinding bodies, which are as a rule very small. When the grinding stock passes through these relatively narrow openings, which form as a whole a narrow passage cross-section, into the regularly relatively large cross-section of the separating device, a strong reduction of the flow speed of the grinding stock occurs. This leads to a strong reduction of the shearing in the grinding stock. Therefore so-called pseudoplastic grinding stocks take on a higher local viscosity. Furthermore the grinding stock distinctly adheres to the separating device because of the large inner surfaces of the separating device. In fact with the agitator mill with a coolable mixing body in the separating device the flow speed is only slightly reduced; however, the viscosity is increased more distinctly due the cooling of the grinding stock. The above-described problems entail difficulties when cleaning the agitator mills by means of rinsing fluid for the purpose of preparation for a grinding stock exchange. Rinsing fluids of this type are as a rule low-viscous. Because of the extremely different rheological characteristics of the rinsing fluid on the one side and of the grinding stock, and that in particular of the pseudoplastic grinding stock, on the other hand, an only poor miscibility is given. During rinsing often conduits are formed; the low-viscous rinsing fluid flows through the accumulation of tenacious grinding stock in the hollow separating device without discharging the grinding stock. Furthermore difficulties also appear due to the fact that grinding stock agglomerates, which are still not completely dispersed when passing once through the agitator mill, can clog the separating device. The same occurs when comminuting relatively rough particulate solids. Also fibres or other foreign particles can lead to the clogging of the separating device.